Add parser state code and skeleton for the parsing procedure.

include/parser.h

@@ -0,0 +1,16 @@
+#ifndef LIBABACUS_PARSER_H
+#define LIBABACUS_PARSER_H
+
+#include "table.h"
+#include "ll.h"
+#include "tree.h"
+
+/**
+ * Parses the given list of tokens into the given tree pointer.
+ * @param tokens the tokens to use for parsing.
+ * @param string the string to use for determining token values.
+ * @param store_into tree pointer to store the new data into.
+ */
+libab_result parse_tokens(ll* tokens, const char* string, tree** store_into);
+
+#endif